The relation of contractile and food vacuoles to rhythms in Paramecium

Experiments were undertaken to determine the relation between metabolic activity, as indicated by the rate of contractile vacuole pulsations and the size and number of food vacuoles formed, and the occurrence of rhythms in the division rate. The animals studied were pedigree races of Paramecium aurelia and Paramecium calkinsi. Two cultures of each species were studied for 115 days under constant culture conditions. Observations were made daily and averages computed for the per diem division rate, food vacuole number and size, and the pulsation rate of the anterior and posterior contractile vacuoles. In Paramecium aurelia, depressions in the rate of contractile vacuole pulsation are, in general, synchronous with the low points of the rhythms in the division rate and with the occurrence of endomixis. The posterior contractile vacuole pulsates more rapidly than the anterior. The variations in the number of food vacuoles formed are, in general, synchronous with the rhythms in the division rate and the fluctuations in the rate of pulsation of the contractile vacuoles. Although endomixis does not occur in Paramecium calkinsi; this species exhibits definite fluctuations in the rates of the two contractile vacuoles which corresponds to the rhythms in division rate. The anterior and posterior contractile vacuoles show no significant difference: in rate. As in P. aurelia, the fluctuations in the number of food vacuoles formed in P. calkinsi is synchronous with the rhythms in reproductive activity and the fluctuations in contractile vacuole pulsations. Paramecium calkinsi forms more for vacuolles than Paramecium aurela, though the size of the vacuoles is smaller in the former. The rate of pulsation of the contractile vacuoles is faster in P. aurelia than in P. calkinsi; a difference probably correlated with the smaller size of P. calkinsi.